Travelling wave tube



y 3 1956 N. w. ROBINSON ET AL 2,757,310

TRAVELLING WAVE TUBE Filed Dec. 30, 1952 IN VEN TORS NORMAN WRIGHT ROBINSON By ALEXANDER TURP/E ZZLD HUTCH/NS N AGENT United States Patent 2 ,757,310 TRAVELLING WAVE-TUBE Norman Wright Robinson, Carshalton Beeches, England, Alexander Turpie, Midlothian, ScotlanrL-arrd .Harold Hutchinson, Wallington, England, assignors to Hartford National Bank and Trust Company, Hartford, Conn, as trustee Application December 30,1952; Serial Nor-328,582

Clairnsprro'rity, application Great Britain'January '1, 1952 TCIaims. (Cl'. 315 3.5)

The invention-relates to. a travelling-wave: tube comprising a conductive electric wave-retarding helix, which is supported by one or more elongated stay members, which: engage the. helix at a small number of'p'oin'ts. at each turn.

A known construction has a number of insulating rods, whichv are regularly distributed about the circumference of the helix" andare fixed inposition. relatively to one another. A- further construction has a tube of glass, quartzor ceramic material, having a' polygonal sectional area.

The known constructions have the advantage that the quantity of insulating material in'the field of the helix, havingia comparatively high. dielectric constant is at a minimum, so that aminimum.fielddistortion iszen'sured.

For helical conductors. of. small. diameters itlis often difiicult to use the known constructions in a simple manner, particularly, if the helix is supported on the inner side. In this case the annular electron beam travels along the outside.

According to the invention, a travelling-wave tube comprising a helical conductor, supported by an insulating support engaging the helix only at a small number of points at each turn, comprises a stay member, of which the points of contact with the turns of the helix are themselves located on a helical line.

The construction in accordance with the invention permits of minimizing the quantity of insulating material in the field of the helix.

The stay member may be constituted by an elongated, flat strip which is wound helically about its centre line or about one of the short sides. Two contact points or one contact point are then obtained respectively on each turn. The strip may be made of ceramic material and be wound during the spraying operation. If the helical conductor is comparatively long, be provided with a stiffening part, which is also made of insulating material, i. e. a cylinder if the conductive helix is supported on the outer side and a rod, if the helix is supported on the inner side. If the conductive helix has in turns and the support n2 turns, the number of contact points per turn of the conductive helix is (n1in2)/n1, Where the minus sign is used if the helices are both wound in the same direction and the plus sign is used, if one helix is wound in clockwise direction and the other in anti-clockwise direction.

In order that the invention may be readily carried into eifect, it will now be described in detail with reference to the accompanying drawing, in Which Figs. 1 and 2 relate to a travelling-wave tube comprising an internally supported helix, intended for connection to hollow wave guides,

Fig 3 relates to a tube intended axial cables and Figs. 4 to 9 relate to an internal support consisting of a flat wound strip.

Referring to Figs. 1 and 2, the wave tube is designated by 1, the

for connection to cowall of the travellingannular cathode by 2 the helical support may and the-focusing. electrode by 3. The first anode 4 is constituted by a perforateddisc and has: two inward pi 'ojectingextensions' 5 to support the conductivecylinder 6; this hollow cylinder is also supported by a. supporting disc 7: The-:current is supplied to theelectrodes through anpluralityof. pins taken through the bottom 8': and of which one, designated. by 9, intended for the electrode 3is shown. At the'end of the tube remote fromxthe cathode provision is made of a conductive hollow'cylinder.'10, .two-stay rings 11 and 12, which are. provided with the-:sameextensions as the anode.4, and acollecting electrode 13, connected to a connecting 'pini14- at .the top of the tube15: The discs 4-and11 arelprovidediwith' cylindrical flanges, having a length of a quarter wave of the oscillations to be produced or amplified by the tube. The fcylinders6' and 10"have an internal'supportiug helix of insulating material16, in this case glass: The helix: 16': supports'the helix-conductor 17; the geometrical internal-cylinder ofwhich corresponds to the geometrical outer'cylirrderl of the helix 16. The weld between the cylindersrdandlfl and the helix are located inside these cylinders. Reference numeral 19 designated the electron path (shown in' broken lines) Theitube shown in Fig. 3 corresponds substantially to thatishownin'Figa 1, so'that corresponding'parts are'de signatedi' by the same reference'numerals. In' this case the cylinders: 6 and'lli' are sealedin the tube wall; so that they need'inoti belsupported." Therefore the anode discLZl). has: no extensions. Reference numeral 22 desigrates? the: insulation. of the: anode supply wire fromthe focusing electrode 3. At 23 is indicated how the pitch of the helix increases gradually towards the ends and terminates in the conductor 24, which forms the input cable and the output cable together with the cylinders 6 and 10 respectively.

Figs. 4, 5 and 6 show a conductive helix 30, which is supported by a flat ceramic strip 31. Figs. 5 and 6 are cross sections taken at the points B and C of Fig. 4. Figs. 7, 8 and 9 differ only so far from the three preceding figures that the ceramic strip 32 has a double width.

The glass helix of the tubes of Figs. 1, 2 and 3 may be manufactured as follows. A rustproof steel rod or a copperplated tungsten rod are enveloped helically by a glass rod. After the copper, if any, has been dissolved, the rod is withdrawn from the helix. If the glass helix is intended for external supporting over greater lengths, it may be surrounded by a glass cylinder, which is slightly elongated after having been weakened, so that it applies itself about the turns of the glass helix. If the glass helix is intended for internal supporting a helical conductor, it may be filled out by synthetic resin or natural resin so as to form a cylinder which may be ground accurately to measure in a centre-less grinding machine or in a different way.

What we claim is:

1. A travelling wave tube including electron beamforming means, a helically-Wound electric wave-retarding conductor, an insulating support for said helical conductor comprising a helical member having a plurality of helical turns disposed within said helical conductor and extending parallel thereto, the outer diameter of said helical member being substantially equal to the inner diameter of said helical conductor, said helical member having a finite and greater pitch than said helical conductor over at least part of its length, whereby the member supports the conductor along different peripheral portions thereof and the point of contact between each helical turn of the conductor and the member is peripherally separated by a significant amount from the point of contact of the member and the adjacent helical turn of the conductor.

2. A travelling wave tube including a helically-wound electric wave-retarding conductor, an insulating support for said helical conductor comprising a helical rod having a plurality of helical turns disposed within said helical conductor and extending parallel thereto, the pitch of said helical rod being finite and substantially greater than the pitch of said helically-wound conductor and the outer diameter of said helical rod being substantially equal to the inner diameter of said conductor, whereby the rod supports the conductor along difierent peripheral portions thereof and the pont of contact between each helical turn of the conductor and the member is peripherally separated by a significant amount from-the point of contact of the member and the next adjacent turn of the helical conductor, and the points of contact lie along a helical line, the number of points of contact per turn of the helical conductor being given by the expression where m is the number of turns of the helical conductor and n2 is the number of turns of the member.

3. A travelling wave tube including electron-beam forming means, a helically-wound electric-wave-retarding conductor, an insulating support for said helical conductor comprising a helically-twisted fiat strip having a plurality of helical turns disposed within said helical conductor and extending parallel thereto, the pitch of said helical strip being substantially greater than the pitch of said helically-wound conductor and the outer diameter of said helical strip being substantially equal to the inner diameter of said conductor, whereby the strip supports the conductor and the point of contact between each helical turn of the conductor and the strip is peripherally separated by a significant amount from the point of contact of the strip and the next adjacent turn of the helical conductor, and the points of contact lie along a helical line, the number of points of contact per turn of the helical conductor being given by the expression (niinz) /m where m is the number of turns of the helical conductor and n2 is the number of turns of the strip.

4. In a travelling wave tube as claimed in claim 3 in which the helically-twisted strip is symmetrical about a line through the center thereof.

5. In a travelling wave tube as claimed in claim 3 in which the helically-twisted strip is symmetrical about a line passing through an edge of the strip.

6. In a travelling wave tube as claimed in claim 3 in which the strip is constituted of ceramic material.

7. In a travelling wave tube as claimed in claim 1 in which a cylindrical insulating body supports the helical member.

References Cited in the file of this patent UNITED STATES PATENTS 2,064,469 Haefi Dec. 15, 1936 2,110,911 Knoll et al. Mar. 15, 1938 2,300,052 Lindenblad Oct. 27, 1942 2,351,055 Lakhoosky June 13, 1944 2,452,572 Iago Nov. 2, 1948 2,489,082 De Forest Nov. 22, 1949 2,653,270 Kompfner Sept. 22, 1953 2,672,572 Tiley Mar. 16, 1954 FOREIGN PATENTS 668,017 Great Britain Mar. 12, 1952 984,595 France Feb. 28, 1951 993,156 France July 18, 1951 

